Field-effect transistors with high frequency capability, i.e. in the 1 to 20 GHz range, have been known. And the upper frequency and power output capability of RF power transistors has been steadily increasing. Schottky barrier gate, field-effect transistors are particularly compatible with high frequency operation because their geometry and gate response permits minimization of parasitic reactance and impedance. However, these transistors have typically been high-Q, narrow band amplifiers, see U.S. Pat. No. 3,516,021. Broadband operations, i.e. greater than one octave in width, of such transistor have not been made possible without the use of complicated supporting circuitry, see "GHz Amplifiers-How They Are Practical", EDN July 15, 1970, p. 41.
Specifically, broadband capabilities are complicated by device characteristics such as low input resistance, gain-frequency variations, and package parasitics and particularly base lead inductance. Broadbanding of RF power transistors has thus required impedance matching of both input and output, together with provisions for gain-frequency compensation. Input and output transformers have been used to match the impedance of the device to the external circuit impedance, which is generally between 25 and 100 ohms and typically 50 ohms, without power loss. Gain-frequency compensation has been accomplished by (1) the use of frequency selective dissipative matching networks, (2) use of frequency selective load mismatching, and (3) use of frequency selective input mismatching. And lead parasitics have been eliminated by the use of coaxial cables and microstrips, see Electronics Design 1, Jan. 4, 1970, p. 100.
The present invention overcomes these difficulties and complications of the prior devices. It provides a high frequency, Schottky barrier gate, field-effect transistor capable of maintaining a substantially constant impedance over at least an octave of frequency variation. Further, it provides a field-effect transistor which can match the impedance of generally used circuits, i.e. 25 to 100 ohms, and which is readily adaptable for use with microstrip leads.